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Friday, January 26, 2007

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The Blu-ray Disc Association has added the MPEG-4 AVC and VC-1 video codecs to its specification for prerecorded Blu-ray Disc media, it says this week.

Blu-ray Disc is one of two formats vying to become the de facto optical disc standard for high-definition video.

As a result, the two codecs will form part of version 1.0 of the BD-ROM logical format, which is expected to be finalized later this year, says Richard Doherty, Panasonic Hollywood Labs' managing director of Blu-ray and professional A/V (audio/visual). The logical format specifies the way in which content is stored on the disc. The physical format, which concerns technical specifications for the disc itself, was already approved in July this year.

VC-1, the proposed Society of Motion Picture and Television Engineers standard, is based on Microsoft's Windows Media 9 codec, and was previously called VC9, says Doherty. MPEG-4 AVC is based on the H.264 codec.Greater Flexibility

All Blu-ray players will be required to support playback of MPEG-4 AVC and VC-1, in addition to MPEG-2. The main advantage of requiring two codecs to the specification is it allows greater flexibility to content providers to pack more content on a disc. This is because the newer codecs are more efficient at compressing data than the MPEG-2 codec that's used with the rewritable Blu-ray Disc format and so allow more video to be stored in the same amount of space.

In the case of a 25GB single-layer Blu-ray Disc, about two hours of video encoded in MPEG-2 at a data rate of between 23 megabits per second and 25 mbps can be stored, Doherty says. MPEG-2 is used in DVD-Video and the first generation of the rewritable version of the Blu-ray Disc format. In contrast, the two new codecs can achieve an equivalent quality of video at about half the data rate and so expand the 25GB disc's capacity to up to 4 hours, he says.

"There are other advantages to having two compression techniques," Doherty says. "Moving forward, the technologies can have competition to help drive down licensing fees and improve picture quality."

HD-DVD (High Definition/High Density-DVD), the main competitor to Blu-ray Disc, has already made the two codecs part of its standard for prerecorded discs. In June companies supporting HD-DVD trumpeted this as one of its advantages over Blu-ray Disc.

"With this adoption, all that [advantage] is gone," says Doherty.

Adoption of the advanced codecs in future versions of the BD-RE rewritable format depends as much on technology as standardization talks, says Doherty. High-definition broadcasting in Japan and the U.S. uses the MPEG2 format, and current recorders put this broadcast data stream directly onto the disc. Using one of the two new codecs would mean real-time hardware transcoding, and that's too difficult to do in a consumer-level machine at present, he says.